As an electrolyte constituting an electrochemical device such as a battery, a capacitor and a sensor, an electrolyte solution or a polymer electrolyte in the form of a gel containing the electrolyte solution has hitherto been used in view of the ionic conductivity. However, pointed out are problems, for example, that there is a fear of damage of an apparatus arising due to liquid leakage of the electrolyte solution and that the electrolyte cannot be used at high temperature in view of safety. To the contrary, a solid electrolyte such as an inorganic crystalline substance, inorganic glass, and an organic polymer substance is suggested. The organic polymer substance is generally superior in processability and moldability and the resulting solid electrolyte has good flexibility and bending processability and, furthermore, the design freedom of the device to be applied is high and, therefore, the development thereof is expected. However, the organic polymer substance is inferior in ionic conductivity to other materials at present.
The discovery of ionic conductivity in a homopolymer of ethylene oxide and an alkaline metal system causes the active researches of a polymer solid electrolyte. Consequently, it is believed that a polyether such as polyethylene oxide is promising as a polymer matrix in view of high mobility and solubility of metal cation. It is expected that the ion migrates in an amorphous portion of the polymer other than a crystalline portion of the polymer. In order to decrease the crystallinity of polyethylene oxide, various epoxides are copolymerized with ethylene oxide. U.S. Pat. No. 4,818,644 discloses a solid electrolyte comprising a copolymer of ethylene oxide and methyl glycidyl ether. However, the solid electrolyte does not always have satisfactory ionic conductivity. As a measure for solving such problem, developed is a battery which comprises gel polymer solid electrolyte comprising an electrolyte solution and polyethyleneglycol diacrylate. In this battery, a reactive monomer having low molecular weight of a few hundreds to a few thousands is reacted, and it is difficult to completely conduct the reaction. The presence of unreacted polyethyleneglycol diacrylate in the battery has the disadvantage that the properties of the battery are significantly deteriorated (JP-A-11-214038). Disadvantageously, the thermal stability is poor and the properties of battery are deteriorated, in the case that the batteries comprising the gel polymer solid electrolyte containing an electrolyte solution, which have been practically used are operated at a high temperature. Accordingly, the upper limit of use has been limited to about 50° C.
JP-A-9-324114 proposes an attempt to use a polymer solid electrolyte in which a specified alkaline metal salt is incorporated into a crosslinked material of high molecular weight diethyleneglycol methyl glycidyl ether/ethylene oxide crosslinked material. However, this electrolyte cannot give a practically sufficient value of conductivity.